GB638642A - Improvements in or relating to x-ray tubes and energising systems therefor - Google Patents

Abstract

638,642. X-ray tubes. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. July 31, 1947, No. 20797. Convention date, July 22, 1942. Addition to 624,332. [Class 39 (i)] X-ray apparatus as described in the parent Specification also comprises an anode 6, cathode 18 and auxiliary electrode 10, the metallic terminals 8, 20, 26 or lead-in wires are spaced apart outside the envelope less than the sparking-over distance at the applied voltages, and the device is energized for such short periods of time that no ionization of the air between the terminals 8, 20, 26 or lead-in wires can take place. Preferably, a cold cathode is used, the starting discharge being between the auxiliary electrode and the cathode. The auxiliary electron discharge is started by the discharge of a bank of condensers 36, at which point the potential of the starting electrode is approximately equal to anode potential; when the auxiliary electron discharge has started, the starting electrode goes down to cathode potential, due to the resistance 42. The auxiliary electrode 10, Fig. 4, comprises a metal sleeve 12 clamped over a vitreous tube 9 by a collar 13, and a block 14 with an oval hole 16 within which is set the cathode 18, which may be a rectangular thorium or molybdenum plate. The terminals 8, 20, 26 may be of copper or of an alloy whose coefficient of expansion closely approximates to that of the vitreous envelope. In a modification, Figs. 5, 6 (not shown), the leading-in conductors are sealed directly to the envelope and screw into the electrode assemblies. In another modification, Fig. 7 (not shown), the lead to the auxiliary electrode is sealed into a side arm of the device, and in yet another modification, Fig. 8 (not shown), the leads to the cathode and control electrode are taken out through a single pinch. The Specification as open to inspection under Sect. 91 states that the electrodes may be assembled with correct spacing outside the envelope and sealed in as a unit. This subjectmatter does not appear in the Specification as accepted.